How to properly create hollow text letter suitable for 3D print?
To create a hollow letter :


create a new project and remove the cube
Add a text object
press TAB to enter Edit mode
change the text to the letter your want
press TAB to exit Edit Mode
press ALT + C and select "Mesh from curve/meta/surf/text"
press TAB to enter Edit mode
press A to select all vertices
press E to extrude to the alf of the final letter depth
press Shift + S and select "Cursor to selected"
press X to delete faces
press TAB to exit edit mode
select menu "Object / Transform / Origin to 3D cursor"
add a solidify modifier
change the thickness
apply the solidify modifier
press TAB to enter edit mode
change the view to Front Ortho (5 1)
press Z to change to Wireframe display
press B and draw a border to select faces on the top of your letter

press X and select "Faces"
press Z to come back to Solid display
press TAB to exit Edit mode
add a mirror modifier
select the proper option X/Y/Z (unselect X and select Z)
apply the mirror modifier